Liquid filtration apparatus and method embodying super-buoyant filtration particles

ABSTRACT

Presented is a liquid filtering apparatus and method that overcomes the disadvantages encountered with prior bed filtration systems by providing a filtering apparatus that incorporates a super-buoyant filter medium having a specific gravity very substantially lower than that of the process liquid being filtered. This feature enables a majority of the medium to float on top of the process liquid. Due to the significant differences in specific gravity between the media and the process liquid, super-buoyant media produce a highly advantageous means of naturally, gravimetrically separating both clean and contaminated filter media and process liquid into separate “phases”. Under normal filtering operation, the filter media is contained within a filter housing by a bed support near the top of the filter housing, and particulate material is filtered from a process liquid that passes through the housing. To regenerate the filter media, the housing is drained and a nozzle creates a backwash spray that washes the particulate material from the filter media. During the backwash process, the filter media rises past the nozzle as the level of the backwash liquid in the housing rises, so that the entire filter media is regenerated.

The invention described and claimed herein is related to co-pendingapplication Ser. No. 09/433,910 filed Nov. 3, 1999 by the inventorherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and method for filteringparticulates of various sizes from miscellaneous process liquids, andmore particularly to an apparatus and method that utilizes a filtrationbed formed from super-buoyant media, which has a specific gravity muchlower than that of the liquid being filtered.

2. Description of the Prior Art

A preliminary patentability and novelty search regarding the inventiondescribed herein has revealed the existence of the following UnitedStates Patents: 3,067,358 3,469,057 3,678,240 3,709,362 3,962,5574,032,300 4,198,301 4,383,920 4,387,286 4,415,454 4,417,962 4,608,1814,743,382 4,839,488 4,865,734 4,883,083 4,952,767 4,963,257 5,030,3535,122,287 5,126,042 5,178,772 5,217,607 5,227,051 5,232,586 5,573,6635,747,311 5,770,080 5,833,867 5,932,092 5,945,005 6,015,497A careful review of the patents noted above has failed to reveal theconcept, apparatus and method disclosed herein.

The need to remove particulates, whether contaminants or products, fromprocess liquids is common to a wide range of processes. In the followingdescription, the focus will be on the removal of particulatecontaminants from water-based process liquids, such as swimming pools,aquariums, or sewage treatment effluents, from the deionized water usedduring electrical discharge machining (EDM), or from aqueous solutionssuch as the coolants used during conventional machining. However, thesame filtration mechanism can be applied to the removal of contaminantsfrom a variety of other process liquids including paints, oils, andhydraulic liquids. The mechanism can also be applied to the filtrationand harvesting of particulate materials that form the product(s) of aprocess and are suspended in a process liquid.

Although a variety of methods have been developed to remove particulatesfrom such process liquids, the most popular method is media filtration.In media filtration, particulate contaminants are strained from theprocess liquid in one of two ways, either by pumping the contaminatedliquid through a unitary permeable element, or by pumping the liquidthrough a filter bed that is itself composed of small particles.

In permeable element filtration, the liquid is pumped through an elementwhich has pores or channels that allow the liquid to pass through theelement but prevent the passage of particulates larger than thepore/channel diameter. Permeable elements comprise a variety ofmaterials, including fabric, paper, ceramic, metal, and plastic. Theseelements filter the liquid primarily by capturing the contaminantparticles on the surface of the element, thus building up a crust orlayer of contaminants on the surface. As contaminants accumulate on thesurface of the element, liquid flow through the permeable element isreduced because the crust or layer of contaminants acts as anobstruction and because an increasing number of the pores or channelsbecome blocked. As the percentage of blocked pores/channels increasesand the crust or layer of contaminants becomes thicker, the pressurerequired to maintain a specific rate of flow of liquid through theelement increases. Eventually, the pressure required exceeds thecapability of the pump, or some other system component, and thecontaminated element must be replaced with a new element in order tomaintain the desired performance of the filtration system.

Alternatively, an attempt may be made to clean the filter element (e.g.,by backwashing it with clean liquid or air) to remove the contaminantsaccumulated on the surface. However, even when the contaminantaccumulation on the surface of such an element is removed, there areusually contaminant particles that remain lodged in the permeableelement that cleaning is not totally successful in removing. Ultimately,the element must either be replaced with a new element or cleaned in amore rigorous fashion, i.e. by immersion in an acid or base solution todissolve the contaminants. The more frequently such element replacementor stringent cleaning must be performed, the more costly this filtrationprocess becomes.

In contrast, the second type of media filtration, namely bed filtration,uses a filter bed composed of small particles such as sand ordiatomaceous earth, and is one of the most common conventional methodsof removing particulate contaminants from liquids. The sand filter usessand particles that are about 0.35 mm in diameter and fairly uniform insize. Diatomaceous earth filters use a siliceous material formed fromthe skeletons of small (about 100 microns [μm] in diameter) marine algalcells called diatoms. Both sand and diatomaceous earth filters use mediathat are substantially heavier than the process liquid being filtered,so that the media sink to the bottom of the filtration vessel forming abed of filter media. This bed may range from several inches to severalfeet in thickness. Nominally, in a conventional bed filter, the processliquid is pumped, or allowed to flow (via gravity), downward throughthis filter bed. As the particulate-laden liquid passes through the bed,the particulates are strained from the liquid and the cleaned liquidexits at the bottom of the bed.

The bed removes the particulate contaminants via one of two processes.First, the larger particulates, which are unable to pass through thespaces between the bed grains, are trapped at the top surface of thebed. This straining effect produces a layer or crust (also called acake) of large contaminant particles, which builds up on the surface ofthe bed, a mechanism called surface filtration. This cake can actuallyenhance the performance of the bed by helping to capture morecontaminant particulates, which are retained in the crust itself,because they cannot pass through the spaces between the contaminantparticles that form the crust.

Second, smaller particulates, which are carried into the bed by theliquid flow are intercepted by the bed's grains as they follow theconvoluted flow pathways taken by liquid as it passes through the bed, amechanism called depth filtration. Although smaller particulates arecaptured in the bed material, the smallest particulates may not becaptured, as they can continue to flow through the bed and exit with thesemi-cleaned liquid at the bottom of the filter bed.

Ultimately, the particulates sequestered by the bed accumulate, makingit more difficult for liquid to flow downward through the bed, and thusthe flow rate declines. The pressure required to force liquid throughthe bed then increases, and presents an excellent indication of thegrowing need to cleanse the bed of the accumulated particulates.Cleansing is achieved by a process of backwashing or back flushing.

During backwashing, clean liquid is vigorously pumped upwards from thebottom of the particulate bed. This upflow of liquid causes the bed toexpand slightly, freeing the captured particulates and washing themupwards and out of the bed. As the bed expands, the bed particles haveless interference with each other and thus settle faster, matching theup-flow rate of the liquid. This effect prevents the bed particles frombeing washed out of the bed along with the contaminant particulates.Typical backwash conditions are 5 to 15 minutes duration with the bedvolume expanded 15 to 30%.

Although sand and diatomaceous earth filters have been successfullyapplied to a wide variety of filtration problems, they have a number oflimitations and drawbacks. One of the most serious problems involvesmaintaining bed homogeneity during operation. Inhomogeneities in the bedinclude, for example, cracks that offer regions of less flow resistance.Such cracks lead to the formation of channels in the bed, poordistribution of the liquid flow through the bed, and thus very lowparticulate removal. Such inhomogeneities may also allow air to betrapped in the bed, also leading to the formation of channels and poordistribution of the liquid.

In addition, the size and cleanliness of the bed particles are extremelyimportant to the success of the filtration process; a bed composed oflarge particles allows significant numbers of small particulates to passthrough the filter bed along with the process liquid. On the other hand,beds composed of smaller particles can quickly become clogged with smallcontaminant particles, thus rendering the filter bed ineffective. Thebed particles can also adsorb organic compounds on which microorganismsfeed. Microbes growing on these organic compounds can bind the filterparticles together and clog the bed, thus decreasing its effectivenessand shortening the interval until cleaning.

To maintain cleanliness, large volumes of clean liquid are required tobackwash and clean conventional filter beds, leading to large volumes ofcontaminated liquid which must be treated or properly disposed. Eventhough backwashing is fairly effective for removing many of theparticulates captured by the filter, some particulates may adhere sostrongly to the bed particles that they are virtually impossible toremove. These residual contaminants reduce the effectiveness of thefilter and significantly impair filter performance. Additionally, thespecific gravity of the contaminant particulates is often equal to orgreater than the specific gravity of the particles that make up thefilter bed. In such circumstances, it is impossible to separate theheavy contaminant particles from the bed particles through a backwashprocess, and backwashing is therefore not effective as a cleaningmethod.

Thus, one of the most crucial problems with these systems, which iscommon knowledge to practitioners of this art, is the ineffectiveness ofbackwash systems for cleaning the filter media (i.e., Amirtharajah,1978). As a consequence, in many situations, the contaminated bed cannotbe cleaned and instead must be replaced with new bed material. In fact,during normal operation, both sand and diatomaceous earth filtersrequire that the media be discarded after a certain level of mediacontamination has been reached. In applications that involve heavyparticulate contaminant loads in the process liquid, these media mayhave to replaced on a daily or weekly basis, which is not economical.

An alternative method of bed filtration uses a filter bed composed ofbuoyant filter media particles. In this method, the media form a bed inwhich the majority of the media floats just beneath the surface of theprocess liquid. The process liquid is pumped into the bottom of thefilter chamber and flows vertically upward through the bed. As theprocess liquid passes through the bed, contaminants are filtered fromthe liquid via the surface and depth filtration mechanisms describedabove.

Prior applications of this buoyant media method to the filtration ofwater (e.g., Banks, U.S. Pat. No. 4,885,083, Hsiung, et al., U.S. Pat.No. 4,608,181) have described the use of a filter media with a specificgravity of 0.7 to 0.8 or greater. For example, in Hsiung et al., themedia is exactly defined as having a specific gravity of no lower than0.8 and “most preferably” no lower than 0.9. Banks precisely specifiesthe specific gravity of buoyant media as 0.75 to 0.9, and “substantiallyequal to 0.90 to 1.0”.

Nominally, the buoyant media particles used in this type of applicationare also of a larger diameter than the media particles used in eithersand or diatomaceous earth filters. For example, Hsiung, et al. specifythe particle diameter as being preferably in the range of 1.5 to 20 mm,in contrast to the sizes of sand particles (about 0.35 mm in diameter)and diatomaceous earth (about 100 microns [μm] in diameter). Due to therelatively large size of the media particles, these buoyant media filterbeds are not optimized to remove small particulate contaminants. Ingeneral, they are designed to perform larger particulate contaminantremoval and some degree of biofiltration of the process liquid by thebacterial biofilm adhering to the media particles.

This buoyant media filter system, as described in the Hsiung et al.patent, actually achieves optimal operation with the media in apartially clean state. In fact, Hsiung et al. write “ . . . it isadvantageous to leave a certain amount of deposited solids in a buoyantmedia filter, as the solids reduce the size of the pores of the filterand assist in filtration”. This requirement is often referred to as“ripening” the filter, and it means that a significant portion of thefiltration capability achieved by Hsiung et al. is provided by thecontaminant particles that were previously filtered and retained by themedia or the microbial biofilm covering the media.

The requirement to use a “ripened” filter media bed dictates that theperformance and operation of the media bed cannot be accuratelycharacterized or predicted, as both depend on the amount and nature ofthe contaminant material(s) previously deposited on the buoyant mediaparticles during the ripening process. This lack of predictableoperation makes it very difficult or impossible to develop an optimaldesign for this type of filter.

In addition, backwashing must be performed in a gentle fashion topreserve the “ripened” layer on the filter media. If the backwash isespecially vigorous, particles that were adhering to the buoyant mediawill be removed from the media and a portion of the buoyant media'sfiltration capacity would thus be lost. That capacity cannot be regaineduntil the filter has “ripened” by again filtering a sufficient amount ofcontaminant particles and retaining them in the filter media in order toreplenish the loss.

Thus, backwashing is typically performed by gently agitating the bedwith air bubbles introduced beneath the bed and allowed to flow upwardsthrough the bed or by gentle streams of water directed into the bed toagitate and dislodge some of the adhering contaminant particles.Accompanied by normal or reduced flow of process liquid through thebuoyant media bed, these backwash methods flush only a portion of theretained contaminants from the filter bed.

The backwash system described by Hsiung et al. is the type that uses airinjection and the normal flow of raw process liquid to wash excessparticulates out of the media. Because the buoyant media particles havea specific gravity close to that of water, it is easy for these gentleagitating mechanisms to move the mostly submerged media around in theprocess liquid, and thus dislodge some of the contaminant particulatesadhering to the media. Consequently, these mechanisms provide therequired minimal degree of cleaning of the filter media bed. Using thismethod of backwashing, the amount of solids flushed from the buoyantmedia depends on total wash volume. However, because the media particleshave a specific gravity close to that of water, they are moved easily bythe backwash mechanism, and cannot be thoroughly cleaned.

Unfortunately the problems encountered in using small diameternon-buoyant media, such as sand or diatomaceous earth, are exacerbatedwhen using small diameter buoyant media. Due to the high surface area ofthe small diameter media, contaminant particles that fill theinterstices between the media particles can act like a glue which makesthe media particles adhere to one another and form clumps which lead tothe formation of non-homogeneities within the bed (just like the problemthat occurs in small diameter non-buoyant media). Because the backwashsystems must be relatively gentle in nature for the filter to retain its“ripened” state, these non-homogeneities cannot be removed from the bed,and the bed performance declines. This problem dictates that smalldiameter filter media not be used in buoyant media applications, becausethe ripening process itself severely limits the efficacy of the filterbed.

In addition, for cost savings, many of these buoyant media filtersystems do not employ a separate backwash pump or backwash water storagesystem. As a result, raw process liquid is used to backwash the bedmedia. In these designs, maximum cleanliness of the media particlescannot be achieved because a separate, isolated pump and process liquidstorage system are not utilized to provide a source of clean processliquid for backwashing. Thus, although such buoyant media filters havedesirable characteristics for specific filtration applications, they donot overcome the above-stated disadvantages of conventional media bedfilters.

In view of the above disadvantages with conventional apparatuses andmethods, it is the principal object of the present invention to overcomethe above-discussed disadvantages associated with prior media liquidfiltration systems.

Another object of the present invention is to provide a liquidfiltration apparatus and method that embodies a filtration bed formedfrom super-buoyant particles having a specific gravity less than onehalf that of the liquid being filtered.

A still further object of the invention is to provide a liquidfiltration apparatus that embodies a filtration bed that floats on theliquid to be filtered.

Yet another object of the invention is to provide a new and improvedfiltering system for the removal of particulate contaminants fromprocess liquids which incorporates a high-efficiency back-washablefilter bed.

A still further object of the invention is the provision of a liquidfiltration apparatus and method that in one aspect incorporates a pairof filtration housings connected in parallel.

Yet another object of the invention is the provision of a liquidfiltration apparatus and method that in another aspect incorporates apair of filtration housings connected in series.

The invention includes other objects and features of advantage, some ofwhich, with the foregoing, will be apparent from the followingdescription and drawings. It is to be understood that the invention isnot limited to the embodiments illustrated and described, since it maybe embodied in various forms within the scope of the appended claims.

SUMMARY OF THE INVENTION

The invention disclosed herein overcomes the disadvantages encounteredwith prior bed filtration systems by providing a filtering apparatuswhich incorporates a super-buoyant filter medium having a specificgravity very substantially lower than that of the process liquid beingfiltered. This requirement permits a majority of the medium to float ontop of the process liquid.

In contrast, as described above, previously-described “buoyant media”filters use filter media which are at or near neutral buoyancy in theprocess liquid, and therefore float with the majority of the media justbelow the surface of the process liquid. For example, Hsiung et al.specifically define buoyant filter media as having a specific gravity ofno lower than 0.8 and “most preferably” no lower than 0.9. Using aspecific gravity value of 0.9, the amount of a buoyant media particlethat floats above the surface of the process liquid can be calculatedusing fundamental physical principles.

Based on a specific gravity of 0.9, a sphere 1 cubic centimeter involume will have a mass of 0.9 grams. If that sphere is placed in water,it will displace 0.9 cubic centimeters of volume. This displacementmeans that 0.1 cubic centimeter of the sphere, or 10%, will be visibleabove the surface of the water as shown in FIG. 1, neglecting surfacetension and other effects described below. Thus, 90% of the buoyantmedia sphere will actually be immersed beneath the water's surface. Ifseveral spheres are stacked on top of one another to increase thethickness of the media layer, the relationship remains the same, so that90% of the media thickness will still be immersed in the water and 10%will be exposed above the water.

In contrast to buoyant media, super-buoyant media form a mass in whichthe majority of the media floats on top of the process liquid (i.e., inwhich the media have a specific gravity less than one-half that of theprocess liquid). For clarity, this difference is illustrated in FIG. 1.The use of super-buoyant media that float principally on top of theprocess liquid is a design feature that provides unique capabilities notprovided by the buoyant media filter designs described in Hsiung, etal., Banks, Muller et al., or any of the other filtration systemsdescribed previously.

It must be emphasized that the distinction between filter media floatingsubmerged beneath the surface of the process liquid and filter mediafloating on the surface of the process liquid is critical in determiningthe unique operational characteristics of the each kind of filter. Forexample, when using buoyant media in water, the filter media (A inFIG. 1) behave principally as though they are part of the water mass.Thus any horizontal movement of the water containing such media dragsthe media along with it. An injection of air bubbles into such a mediabed will also move the media particles because they are very close toneutral buoyancy, and this neutral buoyancy renders them easy to move.

In contrast, super-buoyant media filter particles (B in FIG. 1) do notbehave as though they are part of the process liquid mass. Instead, theyform a mass that floats on the surface of the process liquid, largelyindependent of, and isolated from, the movements of the process liquidbeneath. Horizontal movements of the liquid beneath the floating,super-buoyant media have virtually no effect on the media, and thus suchmovements do not tend to cause significant movement of the super-buoyantmedia bed. In essence, the super-buoyant media described herein behavemuch like a cork floating on a water surface.

To achieve this effect, the super-buoyant media particles must have anominal specific gravity less than 50% of the specific gravity of theprocess liquid to be filtered. In practice, utilizing a super-buoyantmedia with the lowest possible specific gravity maximizes theeffectiveness of both the filtration and backwashing mechanisms. Forexample, in the filtration of particulate contaminants from water, goodperformance can be achieved when the specific gravity of thesuper-buoyant filter media is less than or equal to approximately0.25-0.35, but the best performance is achieved when the specificgravity of the super-buoyant media is in the range of 0.01 to 0.05.These super-buoyant media are typically selected from materials such aslightweight plastics (e.g., expanded polystyrene), or hollowmicrospheres formed from glass or ceramic.

The use of such super-buoyant media insures that nearly all of the bedformed by the filter media floats on top of the surface of the water,with only a minimal amount of the media submerged beneath the surface ofthe liquid (FIG. 1). This is completely different from the physicalbehavior of filter beds composed of buoyant media particles describedpreviously. It is also completely unlike the sand and diatomaceous earthfilter beds described above for water filtration, neither type of whichhave any buoyancy in water.

Due to the significant differences in specific gravity between the mediaand the process liquid, super-buoyant media produce a highlyadvantageous means of naturally, gravimetrically separating both cleanand contaminated filter media and process liquid into separate “phases”.This natural, spontaneous separation is crucial to both sustaining theperformance of the filter bed and to maintaining the effectiveness ofbackwashing such that each backwash cycle produces a reproducibly cleanfilter bed to insure uniform, predictable filter performance.

The uniqueness of the super-buoyant media approach stems from the factthat when such super-buoyant filter media are used, the aggregate forcesacting on the media produce a natural, spontaneous, gravimetricseparation of the filter media and the process liquid into two differentphases. This occurs in the same manner that a well-agitated mixture ofoil and water separates naturally into two distinct phases when amixture of the two is allowed to reach a static equilibrium. Thus, thesuper-buoyant media of the filter described here is one of its mostnovel and unique aspects, as it provides a method for naturally, easily,and efficiently separating the filter media and trapped contaminantsfrom the process liquid.

As described above, implementation of the super-buoyant media methodrequires that the filter media must float principally on the surface ofthe process liquid. This requirement is satisfied primarily by selectingmedia that are much lighter in density than the process liquid. Thus,selection of the appropriate media to implement this filtration methodmust be initially dictated by the specific gravity of the processliquid. However, selecting media with a low specific gravity is notalways sufficient to identify an optimal filter media for filtration ofa specific process liquid. Other factors can also influence theeffectiveness of the super-buoyant media as a filter for a given processliquid, and therefore must also be considered in selecting the type offilter media.

One of the additional factors in super-buoyant media selection is theattraction of the filter media and the process liquid for one another.For example, when the process liquid is water, hydrophilic filter media(which tend to maximize surface contact with water) will behave in amuch different fashion than will hydrophobic filter media (which tend tominimize surface contact with water). Due to the attractive effect,hydrophobic media and the process liquid tend to separate into twophases more quickly. As a consequence, in conjunction with the buoyancyeffects described above, hydrophobic super-buoyant media typicallyprovide a better filter in water or a water-based process liquid thanwill hydrophilic media.

The second factor in selecting the type of super-buoyant filter media isthe attraction of the filter media particles to one another. If, forinstance, there is a weak electrostatic attraction between the filtermedia particles, the particles tend to adhere to one another. As aconsequence, through selection of media material (e.g., plastic,ceramic, or glass), this electrostatic effect can be utilized to assistthe filter media in forming a coherent mass that floats better on thesurface of the process liquid, as well as assisting in attraction andremoval of contaminant particles from the process liquid. If theelectrostatic attraction between the media particles is too great,however, the particles will tend to stick to one another too strongly,thus forming clumps that can cause bed inhomogeneities or interfere withthe removal of contaminants from the bed during backwashing. In thislater case, it may be necessary to include in the filter housing, ameans of electrically grounding the media to remove the charge

The third factor to be considered is the geometric shape of the filtermedia particles. The filter bed generally works best when the mediaparticles are uniformly spherical in shape as this shape allows the mostefficient packing of the media particles. Deviations from a sphericalshape can lead to inhomogeneities in the bed, which in turn can decreasethe effectiveness of the filter and significantly complicate cleaning ofthe media.

The final factor that must be taken into account in selecting the typeof super-buoyant media is the nature of the process liquid and thephysical conditions under which the process functions. Practitioners ofthe art will easily recognize that there are many organic solvents inwhich plastic filter media would dissolve, and therefore would not besuitable. In such cases, the use of ceramic or glass microspheres isdictated. In other cases, such as strong acids or bases, the processliquid is extremely corrosive, and corrosion-resistant plastics or glassmicrospheres must be used. In some cases, the process liquid may operateat elevated temperatures or pressures that would rapidly degrade sometypes of plastic filter media, and ceramic microspheres would berequired.

In some situations, once a super-buoyant media has been selected basedupon the factors described above, it may still not be optimal for thefiltration of a particular process liquid. In those situations, it maybe possible to modify the media so that it performs better. For example,the surface of the super-buoyant media particles may be altered bysubjecting the particles to various physical or chemical treatments,including high temperature, high pressure, chemical etching, etc. Thesetreatments are capable of modifying the surface of the media particles,for example, making it more or less hydrophobic in some cases or more orless hydrophilic in others. It is also possible to apply a polymercoating to these media particles. Such polymer coatings may determinethe surface properties of the media directly, or the coatings maycontain additional embedded chemicals that produce different surfaceproperties for the media. These embedded chemicals can be selected tooptimize specific aspects of the super-buoyant media, thus affecting themanner in which the filter functions.

Once the type of super-buoyant media material has been selected basedupon the specific gravity of the process liquid and the othercharacteristics outlined above, it is essential to determine thedesirable size range of the super-buoyant media particles. Ideally, thesuper-buoyant media particles should be as small as possible, and shouldbe chosen based upon the size of the contaminants to be removed.Candidate media are currently available in diameters as small as 10 μmand as large as several cm.

The performance of the filter is also influenced by the thickness of themedia layer. The use of thicker beds composed of larger diameter mediaparticles generally offers good depth filtration. The use of thinnerbeds composed of smaller diameter media particles generally offer goodsurface filtration. By mixing various diameters of media particles andadjusting bed thickness, the efficiency of the filter bed can betailored to meet a variety of filtration problems. Using smallerdiameter media or thicker media beds carry a power penalty, however, asa more powerful, high pressure pump is required to force the processliquid through such a super-buoyant media bed. To resist the pressurerequired to move the process liquid through these beds, a strong,multi-component “sandwich” is used as a bed restraint 16 (FIGS. 2, 3).In both FIGS. 2 and 3, a perforated metal plate 16 a provides supportfor the bed restraint 16. An intermediate layer of coarse screen 16 bprovides additional support as well as facilitates passage of theprocess liquid through the bed restraint 16. The final layer of the“sandwich” is either a very fine mesh screen 16 c (FIG. 2) for medium orcoarse filter media, or a sheet of permeable metal or plastic material16 d (FIG. 3) for fine filter media.

In some situations, a thin layer of super-buoyant media is a preferablechoice for filtering process liquid. In these situations, it may benecessary to insure a uniformly thin media layer by adding a ring grid16 e (FIG. 4) to the bed restraint 16 described above. As describedabove, this bed restraint 16 consists of a perforated metal plate 16 a,an intermediate layer of course screen 16 b and a final layer of finescreen (not shown) or a sheet of permeable metal or plastic material 16d. The ring grid 16 e, in combination with the directed flow of theprocess liquid, or, occasionally, in conjunction with other mechanicalrotating mechanisms, assists in maintaining a uniform, thin media layerto maximize the surface filtration provided by the media. Other griddesigns (e.g., where the open area is filled with small square,rectangular, or hexagonal cells, rather than a single large central openarea), may also be used to assist in maximizing the amount of surfacefiltration achieved.

Smaller media and thicker beds also make it more difficult to clean thefilter when it becomes loaded with contaminants. However, the use ofsuper-buoyant media provides an important and unique advantage in theprocess of cleaning such filter beds to remove trapped contaminants.

The most effective way to clean a super-buoyant media filter bed is touse a rigorous spray of clean process liquid while forcing the entirebed to move through the spray (FIGS. 5A-5F). Beginning with anormally-operating filter (FIG. 5A) in which the process liquid isflowing upward through the media bed 14, cleaning is accomplished byfirst shutting off the flow of process fluid through the filter and thendraining the process fluid from the filter housing 13 (FIG. 5B), thuslowering the level of the process liquid in the filter housing 13 untilthe entire filter bed 14 is below the backwash spray nozzle(s) 44. Next,the drain valve (not shown) is closed and the backwash spray 5 of cleanprocess liquid is turned on (FIG. 5C). As it accumulates in the housing,the level of the process liquid in the filter housing 13 rises (FIG.5D). As the process liquid level in the filter housing rises, thesuper-buoyant media 14 (floating on the surface of the rising processliquid) also rises (FIG. 5E). This forces all of the media in the filterbed 14 to pass through the intense backwash spray 15, which scours eachmedia particle and washes off any adhering contaminants, thus insuringthat each media particle is very thoroughly cleaned. The backwash spray15 is continued until the level of the process liquid in the filterhousing has risen above the backwash nozzle 44 (FIG. 5F). In thecleaning process, all of the contaminants captured by the media bed 14are washed to the bottom of the filter housing 13 for removal. Althoughone backwash cycle is usually sufficient to clean a super-buoyant mediabed, this backwash sequence may be repeated as many times as required toprovide the desired level of media cleanliness. The amount of cleanprocess liquid required for a single backwash is usually no more than2-3 times the volume of the filter media bed.

It should also be noted that although, in the embodiments describedbelow, the filter housing is assumed to be cylindrical in shape, otherhousing shapes may be selected for specific applications to increaseeither or both the filtration efficiency or the backwashing efficiency.Several alternative, non-cylindrical housings 13 a-13 c are pictured inFIG. 6. All of these alternatives provide a larger filtration area and a“necked-down” backwashing section 10. These features enhance the totalarea of the super-buoyant media available for filtration, as well asproviding a means of concentrating the backwash spray to increase itscleaning effectiveness.

The novel backwash mechanism described herein makes it possible tothoroughly scour and clean small diameter filter media, thus providingan unprecedented level of cleanliness in the backwashed media. As aconsequence, the media does not have to be discarded nearly asfrequently as previous filters which used small diameter, non-buoyantmedia, thus making the super-buoyant media filter design significantlymore economical to operate as well as more efficient in removingcontaminants.

The cleaned super-buoyant media bed retains its initial filtrationcharacteristics, and performs in a repeatable fashion after everybackwash cycle, all without requiring any sort of “ripening”. The lifeof the media is also very significantly extended over that experiencedwith non-buoyant media. In addition, because of the high efficiency ofthe backwash mechanism, very little particulate-laden waste processliquid is generated. Thus, this unique, novel backwash method provides acapability that has been lacking in filtration technology, one methodthat has not been directly addressed by any known existing patents orany known products on the market.

During normal operation, the liquid to be filtered is withdrawn from aprocess tank or process stream and pumped under pressure through one ormore filter housings containing the aforementioned super-buoyant bedmedium. The liquid being filtered is pumped into the dry housing at thebottom, elevates the filter bed by floatation to a position wherefurther elevation is restrained and then rises through the restrainedbed medium, exiting the filter housing at the top.

A valve in the exit line at the top of the housing directs the filteredliquid either back into the process tank or stream, or into a cleanliquid storage tank. A small storage tank in the filtration systemprovides a volume of filtered liquid for use in backwashing the filteredmedium to clean it by removing the particulates it strains from theprocess liquid. A valve in the entry line is closed when the backwash isperformed to prevent backflow of contaminated liquid into the processstream. A second valve, in the exit drain line, is opened to direct the“dirty” liquid into a storage chamber where it is collected until it canbe properly disposed or recycled.

In one aspect thereof, the present invention is directed to an apparatusfor filtering particulate contaminants from contaminated liquid processstreams, such as, by way of example, from the deionized water usedduring electrical discharge machining. The apparatus includes a primarypump with a liquid inlet from the process stream or process storage tankand a liquid outlet to the filter hosing a chamber. The filter chamberincludes a liquid inlet from the primary pump and a liquid outlet thatreturns the filtered liquid to the process stream or to a clean processliquid reservoir. The filter chamber contains the filter bed which actsa a strainer to remove the particulates from the process stream.

In another aspect, the present invention is directed to a liquidfiltration apparatus that includes a filter bed composed of aparticulate medium that has a substantially lower specific gravity thanthat of the process liquid to be filtered. The particle size and natureof this bed medium are determined by the identity of the process liquidto be filtered. As the process liquid is pumped through this filter bed,the particulate contaminants are strained from the liquid by one or bothof the aforementioned methods.

In a third aspect thereof, the present invention is directed to a liquidfiltration apparatus that includes a backwash system that incorporates abackwash reservoir to store cleaned process liquid for backwashing, abackwash pump, a single or plurality of backwash nozzles, a backwashvalve, and a backwash waste liquid/particulate collection reservoir.During the backwash cycle, stored cleaned process liquid is withdrawnfrom the backwash reservoir by the backwash pump and forced through thespray nozzles(s). This backwash spray, in conjunction with alternatelyopening and closing of the backwash valve at the bottom of the filterchamber, serves to efficiently clean the strained particulatecontaminants from the bed and wash them into the wasteliquid/particulate collection reservoir.

The above-mentioned and other features and objects of the invention andthe manner of obtaining them will become apparent and the invention willbe better understood by references to the following description ofpreferred embodiments of the invention taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of the difference between buoyantmedia particles (A) and super-buoyant media particles (B) when theparticles are placed into the process liquid to be filtered.

FIG. 2 is a diagrammatic view which presents a detailed view of thefilter bed retaining plates for coarse and medium filter media (meanmedia particle diameter greater than 100 microns [100 μm] in diameter).

FIG. 3 is a diagrammatic view which presents a detailed view of thefilter bed retaining plates for fine filter media (mean media particlediameter less than 100 microns [100 μm] in diameter).

FIG. 4 is a diagrammatic view which presents a detailed view of thefilter bed medium retaining plates for fine filter media (mean mediaparticle diameter less than 100 microns [100 μm] in diameter),incorporating a ring grid to control bed thickness.

FIGS. 5A-5F are a diagrammatic view of the backwash process thatillustrates the various positional relationships of the filter bed tothe backwash spray nozzle during a complete filter and backwash cycle,according to the present invention.

FIG. 6 is a diagrammatic cross-sectional illustration of severaldifferent shaped filter housings which have large surface areas forretaining the super-buoyant media and narrower areas which concentratethe backwash spray to provide maximum cleaning of the media.

FIG. 7 is a diagrammatic view of the overall apparatus for filteringparticulates from a process liquid according to the present invention.

FIG. 8 is a diagrammatic view of the apparatus for filteringparticulates from a process liquid utilizing dual filter housingsconnected in a parallel flow filtration system according to the presentinvention.

FIG. 9 is a diagrammatic view of the apparatus for filteringparticulates from a process liquid utilizing dual filter housingsconnected in a serial flow filtration system according to the presentinvention.

FIG. 10 is a diagrammatic view of the filtration apparatus incorporatingan intermediate hydroxyl ion-generating reactor which functions toprecipitate dissolved metal ions prior to flowing through the filter bedto enable filtering precipitates thereof from a process liquid utilizingthe dual filter, serial flow filtration system illustrated in FIG. 9.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings. The exemplification hereinillustrate preferred embodiments of the invention in specific formsthereof, and such exemplifications are not to be construed as limitingthe scope of the disclosure or the scope of the invention as set forthin the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Single Filter Housing Embodiment

In this embodiment (FIG. 7), a central control system designatedgenerally by the numeral 54 is used to monitor the sensors installed inthe filtration system, and to turn “ON” and “OFF” all of the actuators(pumps and valves) required to operate the system. This control systemmay be operated either by manually actuated switches or by electronicswitches activated by an embedded microprocessor. Although using amicroprocessor makes the system somewhat more complex, it enables moreefficient operation of the system as well as providing unattendedoperating capability during periods when no personnel are available tomanually control the system.

During normal operation, the process liquid to be filtered is withdrawnfrom a reservoir 2, connected by a conduit 3, to a pump priming chamber4. Alternatively, the liquid may also be withdrawn directly from aprocess liquid stream. Although not absolutely required, the use of thepump priming chamber 4 helps prolong the life of the primary liquid pump7, by ensuring that the pump does not run “dry”. Running “dry” (i.e.,run without liquid in the pump head), may damage the pump.

As the liquid is removed from the pump priming chamber 4, through aconduit connecting the pump priming chamber 4 to the primary fluid pump7, a partial vacuum is created in the pump priming chamber 4 and thus inthe conduit 3 connecting the reservoir 2 to the priming chamber 4. Thevacuum pulls process liquid from the reservoir and establishes a supplyflow of the process liquid to the primary pump 7. As the liquid exitsthe primary pump 7, it is pumped through a conduit 8 to a normally-openvalve 9 and into a connecting conduit 11 that attaches to thecylindrical filter housing 13 through the filter housing inlet 12. Itshould be understood that when valves are designated herein, such valvesmay be manually actuated or electronically actuated, and preferably thelatter.

After passing through the filter housing inlet 12, the flowing liquidspreads out, and flows upwards through the filter housing 13, causingthe filter bed 14, which floats on top of the liquid, to rise in thehousing 13. The filter bed 14 consists of small diameter super-buoyantparticles having a specific gravity substantially lower than that of theliquid being filtered, and selected to be within a specific size range,nominally having a diameter between 0.1 micron and 25.4 mm. The size andmaterial composition of the filter bed particles, as well as the bedvolume and filtration area, are determined by the process liquidfiltration requirements, including the size and nature of theparticulates to be removed from the process liquid. The super-buoyantparticles which compose the filter bed are typically formed fromplastic, glass or ceramic materials, but in any event these particlesmust have a specific gravity less than one half that of the processliquid being filtered.

As the process liquid flows into the filter housing 13, the level of theprocess liquid rises in the housing. The super-buoyant media bed 14,which is floating on the rising process liquid, rises until iteventually touches the bed support 16 near the top of the filterhousing. This support restrains [retains] the bed media, and prevents itboth from rising any further in the housing 13 and from flowing out ofthe filter housing 13 along with the liquid being filtered. Although thefilter bed 14 itself is prevented from rising any further in the housing13, the process liquid continues to rise and flows through the filterbed 14 as it is pumped into the housing 13 by the primary pump 7.

As the liquid level rises, the liquid is filtered as it flows upwardsthrough the filter bed 14 and then through the bed support 16 and intothe top of the filter housing. The bed support 16 thus also provides afinal filtration barrier to the particulates carried in the liquid. Thebed support 16 is nominally formed from a multi-layer “sandwich” (FIG.2) comprising a perforated metal plate 16 a, and two or more layers ofscreen 16 b and 16 c. Alternatively (FIG. 3), the “sandwich” may alsocomprise the aforementioned perforated metal plate 16 a, with a singlelayer of screen 16 b, and a layer of semi-permeable membrane or sinteredpermeable plastic or metal material 16 d.

Selection of these constituent layers depends upon the size of thefilter bed particles. The fine mesh screen 16 c or membrane layer 16 dis positioned at the lower face of the bed support 16 immediately nextto the filter bed media. A medium mesh screen 16 b is positioned in thecenter to provide structural support for the fine layer, and theperforated metal 16 a is last and provides structural stiffening for theentire support assembly. The fine material, whether screen 16 c orpermeable membrane 16 d, is preferably the layer that directly contactsthe filter bed media 14. The other layers serve to provide structuralsupport and enhance liquid flow through the bed support 16. Thismultiple layer design provides the strength necessary to retain the bedmedia 14 under working filtration pressures that may be as high, forexample, as 75 to 150 psi. A broader range may of course be utilizedunder appropriate conditions related to the type of media bed, the typeand size of particulates sought to be filtered thereby and the optimumvelocity flow of liquid through the system.

As the process liquid flows vertically upward through the filter bed 14,contaminant particles are retained by the filter bed through one of twodifferent mechanisms. At the point where the process liquid flow firstencounters the filter bed, surface filtration, the first mechanism,occurs. This mechanism occurs as the larger particulates are captured atthe filter bed's lower surface, being unable to pass through the spacesbetween the particles, which make up the filter bed as the liquid flowsup through the filter bed. As these larger particulates are captured atthe lower surface of the filter bed, they form a crust on that surface.

Flowing along with the process liquid, smaller particulates may becaptured at the bottom surface of the filter, retained by the crustformed by the accumulation of larger particulates. Thus, this crust mayby itself prevent the passage of some of the smaller particulates. Someof the smaller particulates may also pass through the crust on thefilter bed's lower surface, penetrate the bed, and become trapped by thesecond mechanism, depth filtration. In this mechanism, these smallerparticulates are captured and retained in the interstitial spaces in thefilter bed between the super-buoyant filter media particles. Thesmallest particles, depending on their size, the size of the bedparticles, and the size of the openings in the bed support, may actuallyflow through the bed and exit the filter housing through the housingexit port 17 along with the out-flowing filtered process liquid.

After flowing through the filter bed support 16, the process liquidenters the top portion of the filter housing above the filter bedsupport structure and exits through the exit port 17. The liquid thenflows through a connecting conduit 23 to a normally-open valve 24,another connecting conduit 26, and a flow sensor 27. Following the flowsensor 27, the liquid flows through an additional conduit 28 connectingto a clean process liquid reservoir 29 where the filtered liquid isstored. Also connected to this conduit 28 through an additional conduit31, is normally-closed valve 32, and a final conduit 33 connected to abackwash reservoir 34. The backwash reservoir 34 provides a means ofstoring filtered process liquid for use in the backwash cycle thatcleans the filter bed medium.

The backwash reservoir 34 is open with respect to the atmosphere throughvent 38 to prevent pressure build-up during filling as well as toprevent creation of a vacuum when liquid is removed for backwashing thefilter. A liquid level sensor 36 in the backwash reservoir 34 isattached to the filter controller 54 via wire 109. The filter controller54 opens valve 32 via wire 110 whenever the backwash reservoir liquidlevel is low, thus allowing filtered process liquid exiting the filterhousing 13 to enter and fill the backwash reservoir 34. When thebackwash reservoir 34 is filled, the level sensor 36 indicates to thecontroller 54 via wire 109 that the reservoir is full, and thecontroller 54 turns off valve 32 via wire 110 to stop liquid flow intothe backwash reservoir 34.

The flow sensor 27 measures the rate of flow of liquid exiting thefilter bed. The signal from this sensor is transmitted to the filtercontroller 54 via wire 112. As the filter accumulates more and moreparticulates from the liquid stream, the resistance of the bed to liquidflow increases, and the flow of process liquid through the filterlessens (unless the flow of process liquid through the primary pump 7 isincreased). At a critical point (defined by the filtration requirementsfor the process liquid), the flow measured by flow sensor 27 is lowenough that the filter must be regenerated by a backwashing process toregain its filtration capacity. This point is identified by having thecontrol system 54 monitor the output of flow sensor 27 via wire 112.

When a backwash operation is required, the normally-open valves 9, 24 inthe filter inflow line and in the filter outflow line, respectively, areclosed by the controller via wires 103 and 111, respectively, to preventcontinued flow of the liquid through the filter. The normally-closedliquid drain valve 46 and the normally-closed atmospheric vent valve 22are opened by the controller 54 via wires 102 and 108, respectively.With these valves open, “dirty” liquid drains from the filter housinginto the collection reservoir 48 through conduit 11, valve 46 andconduit 47 by gravity flow under atmospheric pressure admitted into thehousing through now open vent valve 22.

As the liquid drains into the collection reservoir 48, air enters thefilter housing through valve 22 and conduit 21, and the liquid level inthe housing drops. When the liquid level reaches the bottom of thefilter bed, the super-buoyant bed media 14 (which is lighter than theprocess liquid, and is thus still pressed against the bed support 16 asit floats on top of the process liquid begins to descend in the filterhousing 13 as it floats on the descending process liquid. Filter bed 14is allowed to fall until the top surface of the filter bed has fallenbelow the midpoint of the filter housing 13, as indicated to thecontroller 54 by the lower fluid level sensor 18 via wire 106. At thispoint, the controller 54 closes drain valve 46 via wire 102 and thebackwash spray process is initiated to clean the filter bed.

In the backwash spray process, clean liquid from the backwash reservoir34 is withdrawn through conduit 37 by the backwash pump 39, which isturned on by the controller 54 via wire 104, and pumped through conduit41, normally-closed valve 42 which is now open, and conduit 43, and thensprayed onto the top surface of the now lowered filter bed throughsingle or multiple backwash spray nozzle(s) 44. The number of nozzles 44is determined by the cross-sectional area of the filter bed and theidentity and nature of the filter bed material. A single wide angle,solid cone nozzle with a wide angle of dispersion (e.g., >90 degrees)can easily backwash a filter housing of up to six to eight inches indiameter. Larger diameter housings require multiple spray nozzles foreffective backwashing. When the filter bed consists of extremely fineparticles, it can compress against the lower surface of the bed support16 during filtration, thus forming a hard, compressed layer on thesurface of the filter bed support. In such cases, it is usuallynecessary to have one or more additional spray nozzles that sprayvertically upward to dislodge the compressed bed particles and wash theminto the lower section of the filter housing 13.

The backwash spray delivered by nozzle(s) 44 washes adhering contaminantparticulates off each filter particle of the filter bed 14. As thisspray drains down through the remaining filter bed material, which isnow in its lowermost position, carrying with it the collectedcontaminants, it accumulates in the bottom of the housing. As thisdrainage accumulates, the liquid level in the housing 13 rises, becauseof the continuing backwash process, and the super-buoyant media bed 14(floating on top of the rising liquid) moves upward and past thebackwash nozzle 44 which continues to spray clean liquid into the bed,thus continuously washing out the contaminant particulates, asillustrated in FIGS. 5A-5F. Because these contaminant particulates areheavier than either the liquid or the filter bed particles, the fluidspray washes them out of the bed and causes them to sink to the bottomof the filter housing 13. Simultaneously, the super-buoyant filter bedparticles, which are lighter than the process liquid, continue to floatupwards on the rising liquid level in the filter housing 13.

The backwash spray is continued until the entire filter bed 14 has risenabove the nozzle 44, thus ensuring that all of the filter bed particlesare cleansed by the spray of clean liquid emitted by the nozzle 44.Level sensor 19 indicates to the controller 54 via wire 107 that thelevel of liquid in the housing 13 has risen to the appropriate level,and thus indicates that the entire filter bed has been washed in thismanner.

When the filter controller 54 receives information from the level sensor19 that the liquid level is correct, the controller closes valve 42 viawire 105, opens drain valve 46 via wire 102, and thus causes theparticulate-laden liquid to once more drain into the collectionreservoir 48. This backwash sequence can then be repeated as necessaryto ensure the highest level of cleanliness in the filter bed. Oncebackwashed, the clean filter medium, once again located in the lower endof the filter chamber, is again ready to filter particulates from theprocess liquid stream.

To accelerate the removal of contaminated liquid from the bottom of thefilter housing, it is possible to add a suction pump or siphon tube (notshown) to the system. Such additions easily make it possible to removethe contaminated process liquid from the housing 13 in thirty seconds orless. After backwashing, the filtration process is again initiated bythe controller 54 closing valves 46 and 22 via wires 102 and 108 openingthe inlet valve 9 via wire 103 and the outlet valve 24 via wire 111, andpumping liquid from reservoir fluid pump 7 by actuating pump 7 via wire101. As process liquid again enters the housing, the filter bed 14 againrises in the filter housing until it encounters the bed support 16. Thefiltration process then begins once again as the process liquid beginsto flow upwards through the stabilized filter bed and the particulatecontaminants begin to be captured by one of the two aforementionedfiltration mechanisms.

Parallel Filter Housing Embodiment

Depending on the specific filtration requirements of the process,modifications of the basic single housing filtration system illustratedin FIG. 7 and described above may be required for optimal filtration. Insome processes, for example, it is undesirable or virtually impossibleto temporarily discontinue operation of the filtration process to cleana filter by backwashing. Thus, in this second embodiment of thisfiltration system design, as illustrated in FIG. 8, two filter housings(containing the same type of bed material) are connected in parallelwith one another, so that the filtration system can continue to functionwithout interruption while one of the two filters is being cleaned bybackwashing. In this embodiment, the two filters may be the same size orthe primary filter may be larger than the secondary filter. In theformer case, the two filters may share filtration effort equally, whilein the latter case, the secondary filter serves only as a temporaryfilter to maintain filtration capability during the brief time requiredto backwash the primary filter.

In this embodiment, a central control system 54 with an embeddedmicroprocessor is used to monitor the sensors installed in thefiltration system, and to turn “ON” and “OFF” all of the actuators(pumps and valves) required to operate the system. Although this controlsystem may also be operated manually, due to its increased complexity,the system is much more effectively controlled by an embeddedmicroprocessor. As above, the embedded microprocessor enables moreefficient operation of the system as well as providing unattendedoperating capability for operation during periods when no personnel areavailable to manually control the system.

In this second embodiment, the flow of the process liquid through thefirst or primary filter housing 13 follows the sequence described abovefor the system of FIG. 7. In the interest of brevity in thisdescription, the operational sequence applicable to the embodiment ofFIG. 7 is included herein by reference rather than repeating thesequence.

When backwash of the primary filter 13 is required in this secondembodiment, the normally-open valves 9 and 24 in the primary filterinflow line 11 and in the filter outflow line 23, respectively, areclosed by the controller 54 via wires 103 and 111, respectively, toprevent continued flow of the liquid through the filter 13. At the sametime, the controller 54 opens normally-closed valves 57 and 73 via wires115 and 119, respectively, to initiate the flow of process liquidthrough the secondary filter housing 62. The liquid is pumped by theprimary pump 7 through conduits 8 and 56 to a now open (butnormally-closed) valve 57 and into a connecting conduit 59 whichattaches to the secondary filter housing 62 through the filter housinginlet 61.

After passing through the inlet 61 of the secondary filter housing 62,the flowing liquid spreads out and flows upward through the filterhousing 62, causing the filter bed 63, which floats on top of the risingliquid, to rise in the housing 62. The secondary filter bed 63 iscomposed of the same particles as the primary filter bed 14. Theparticles in the secondary filter bed have the same specific size range,density and composition as the particles in the primary filter in orderto meet the needs of the filtration process.

Alternatively, the primary filter 13 may be larger than the secondaryfilter 62. In the former case, the two filters may share filtrationeffort equally, while in the latter case, the secondary filter 62 servesonly as a temporary filter to maintain filtration capability during thebrief time required to backwash the primary filter 13.

As the process liquid flows into the secondary filter housing 62, thelevel of the process liquid rises in the housing, and the filter bed 63,floating on the rising process liquid, reaches the bed support 64 nearthe top of the filter housing 62. As described above in relation to theembodiment of FIG. 7, this support retains the super-buoyant filter bedmedia, and also provides a final filtration barrier to the particulatescarried in the liquid. The filter bed support 64 is nominally formedfrom the same kind of multi-layer “sandwich” (FIGS. 2, 3) describedabove.

As the process liquid flows vertically upward through the filter bed 63,contaminant particles are retained by the filter bed 63 through surfacefiltration and depth filtration mechanisms. After flowing through thebed support 64, the rising liquid enters the top portion of the filterhousing and exits through the exit port 66. The liquid then flowsthrough a connecting conduit 72 to a normally-closed but now open valve73, another connecting conduit 26, and the flow sensor 27. From the flowsensor, the liquid flows through an additional conduit 28 connected tothe clean process liquid reservoir 29. Also connected to this conduit 28through an additional conduit 31, normally closed valve 32, and finalconduit 33, is the backwash reservoir 34. As the liquid level in thebackwash reservoir 34 descends, it is measured by level sensor 36. Whenthe level reaches a predetermined minimum value, the sensor signals thecontroller 54 through wire 109 to open valve 32 via wire 10. Additionalclean liquid is then added to the backwash reservoir 34 through conduit31, valve 32 and conduit 33. When the liquid level In the backwashreservoir 34 is returned to its normal level, the controller 54 closesvalve 32 via wire 110 to stop the flow of liquid into the backwashreservoir 34.

Once the flow of the process liquid has been directed into the secondaryfilter housing for filtration, the backwash cycle for the primary filterhousing 13 can be initiated. The normally-closed liquid drain valve 46and the normally-closed atmospheric vent valve 22 are opened by thecontroller 54 via wires 102 and 108, respectively. With these valvesopen, dirty liquid drains from the primary filter housing 13 into thecollection reservoir 48 through conduit 11, valve 46 and conduit 47.

As the liquid from the primary filter housing 13 drains into thecollector reservoir 48 during the backwash cycle, air enters the filterhousing through valve 22 and conduit 21, and the liquid level in thehousing drops. When the liquid level reaches the bottom of the filterbed 14, the super-buoyant filter bed material (which is lighter than theprocess liquid, and thus is still pressed against the filter support 16as it floats on top of the process liquid begins to descend in thefilter housing 13 as it floats on the top of the receding liquid. Theliquid level is allowed to descend until the top of the filter bed hasdescended below the midpoint of the filter housing 13. At this point,level sensor 18 signals the controller 54 via wire 106 that the liquidlevel has dropped to the appropriate level, and the controller closesthe drain valve 46 via wire 102 and the backwash spray process isinitiated to clean the primary filter bed as previously explained.

After backwashing of the primary filter bed 14 has been completed, thecontroller re-initiates the filtration process in the primary filterhousing 13 by closing valves 46, 22 and 57, via wires 102, 108 and 115,respectively, and by opening the inlet valve 9 and exit valve 24 viawires 103 and 111, and pumping liquid from the reservoir 2 via theprimary liquid pump 7. As process liquid again enters the housing 13,the filter bed 14 rises in the housing and stabilizes when it encountersthe bed support structure 16. The filtration process then begins onceagain as the process liquid begins to flow upward through the stabilizedfilter bed.

Once the primary filter has been brought back into filtering operation,the secondary filter 63 contained in the secondary filter housing 62 canbe cleaned in the same manner by the backwashing process used for theprimary filter. In the case of the secondary filter, the process beginswhen the controller 54 opens the normally-closed liquid drain valve 58and the normally-closed atmospheric vent valve 71 via wires 114 and 118.With these valves open, dirty liquid drains from filter housing 62 intothe collection reservoir 48 through conduit 59, valve 58 and conduit 47.

As the liquid from the secondary filter housing 62 drains into thecollection reservoir 48, air enters the filter housing 62 through valve71 and conduit, 69, and the liquid level in the housing 62 drops. Whenthe liquid level reaches the bottom of the filter bed 63, the bedmaterial (which is lighter than the process liquid, and thus stillpressed against the bed support 64 as it floats on top of the processliquid) begins to descend in the filter housing 62 as it floats on thetop of the receding liquid. The liquid level is allowed to descend untilthe top of the filter bed has fallen below the midpoint of the filterhousing 62, as indicated to the controller 54 by the lower liquid levelsensor 67 via wire 116. At this point, the controller closes drain valve58 via wire 114 and the backwash spray process is initiated to clean thesecondary filter bed.

To effectively backwash the secondary filter 63, clean liquid from thebackwash reservoir 34 is again withdrawn through conduit 37 by thebackwash pump 39 and pumped through the supply conduit 41, thenormally-closed valve 76 which the controller has opened via wire 113,and conduit 77, and is then sprayed onto the filter bed 63 throughsingle or multiple backwash spray nozzle(s) 78. As explained withrespect to the FIG. 7 embodiment, the number of nozzles 78 is determinedby the cross-sectional area of the filter bed and the identity andnature of the filter bed material. The same backwashing procedure asexplained with respect to the FIG. 7 embodiment continues until theentire filter bed has risen above the nozzle 78, allowing all of the bedparticles to be cleansed by the spray of clean liquid emitted by thenozzle 78. Level sensor 68 then indicates to the controller via wire 117when the level of liquid in the housing 62 has risen to the appropriatepoint, thus indicating that the entire secondary filter bed has beenwashed of all contaminants and particulate matter. When the controller54 receives information from level sensor 68 via wire 117 that theliquid level is appropriate, the controller 54 opens the drain valve 58via wire 114, and the particulate-laden liquid once more drains into thecollection reservoir 48. This backwash sequence can then be repeated ifnecessary to ensure the highest level of cleanliness in the filter bed.The backwashed, clean filter medium 63 is then once again ready tofilter particulates from the process liquid stream. To accelerate theremoval of contaminated liquid from the bottom of the filter housing, itis possible to add a suction pump or siphon tube (neither shown) to thesystem. Such additions make it possible to remove the contaminatedprocess liquid from the housing 62 in less than one minute.

Series Filter Housing Embodiment

In this embodiment, two filter housings are connected in series with oneanother as illustrated in FIG. 9 to provide a filtration capabilitywhich is enhanced over that provided by a single filter. In thisembodiment, the super-buoyant filter bed material 14 in the firsthousing 13 is selected to filter out one or more specific componentswhile the super-buoyant bed material 63 in the second housing 62 isselected to filter out one or more components different from thoseremoved by the first filter. For example, in one specific embodiment,the bed material 14 in the first housing 13 is composed of coarser,larger diameter particles, while the filter bed material 63 in thesecond housing 62 is composed of finer, smaller diameter particles. Thisembodiment allows the first filter bed 14 to serve as a “coarse” filterfor removing larger contaminant particles, and the second filter bed 63to serve as a “fine” filter for removing smaller contaminant, particleswhich remain after the process liquid passes through the first bed 14.By arranging these two filters in series as shown, it is possible tooptimize each filter bed for the removal of specific contaminants andthus to maximize the total amount of contaminant removed by thefiltration system.

In operation, the process liquid to be filtered is withdrawn from thestorage reservoir 2 through conduit 3 to the priming chamber 4, by thevacuum created by the pumping action of the primary pump 7.Alternatively, the liquid may also be withdrawn directly from a processliquid stream. The liquid then passes from priming chamber 4 throughconduit 6 to the primary liquid pump 7, by which it is pumped throughconduit 8, to the normally-open inlet valve 9, and into the connectingconduit 11. Through the connecting conduit 11 in turn, the liquid ispumped into the first filter housing 13 through the filter housing inlet12 as previously described in relation to the FIG. 7 embodiment.

In embodiment of FIG. 9, as in the previous embodiments, after passingthrough the inlet 12, the flowing liquid spreads out and flows upwardthrough the filter housing 13, causing the filter bed 14, which floatson top of the rising liquid to rise in the housing 13. The first filterbed 14 is composed of super-buoyant particles having a specific gravityless than one half that of the liquid being filtered, and selected to bewithin a specific size range, e.g., between 0.5 and 1.0 mm for a“coarse” filter. As with the other embodiments, the size and compositionof the filter bed particles, as well as the bed volume and filtrationarea, are determined by the specific process liquid filtrationrequirements, including the size and nature of the particulates to beremoved from the process liquid. The particles which compose the filterbed 14 are typically formed from plastic, glass or ceramic materials,but in any event these particles must have a specific gravity less thanone half that of the specific gravity of the liquid being filtered.

As previously described with respect to the other embodiments, the levelof the process liquid rises in the housing 13, the filter bed 14, whichis floating on the rising process liquid, rises until it touches the bedsupport 16 adjacent the top of the filter housing. This support 16retains the bed media 14, and prevents it both from rising any furtherand from flowing out of the filter housing along with the liquid beingfiltered. The bed support 16 also provides a final filtration barrier tothe particulates carried in the liquid. As described above, the bedsupport 16 is nominally formed from a multi-layer sandwich (FIG. 2),consisting of a perforated metal plate 16 a, and two or more layers ofscreen 16 b and 16 c or alternatively (FIG. 3), a layer of screen 16 band a layer of semi-permeable membrane or sintered permeable plastic ormetal material 16 d.

Selection of these constituent layers depends upon the size of thefilter bed particles. The fine mesh screen 16 c or membrane layer 16 dis positioned adjacent the lower face of the bed support 16 immediatelynext to the filter bed media, a medium mesh screen 16 b is positioned inthe center to provide structural support for the fine layer, and theperforated metal plate 16 a is last and provides structural stiffening.The fine material, whether screen 16 c or permeable membrane 16 d, isalways the layer which directly contacts the top of the filter bed media14. The other layers serve to provide structural support and enhanceliquid flow through the bed support 16. This multiple layer designprovides the strength necessary to retain the bed media under workingfiltration pressures that may be as high as 75-150 psi, as previouslydescribed. As the process liquid flows vertically upward through thefilter bed 14, contaminant particles are retained by the filter bedthrough two different mechanisms previously discussed. At the pointwhere the process liquid flow first encounters the super-buoyant mediafilter bed, surface filtration, the first mechanism, occurs. Thismechanism occurs as the larger particulates are captured at the filterbed's lower surface, being unable to pass through the spaces between theparticles that make up the filter bed as the liquid flows up through thebed. As these larger particulates are captured at the lower surface ofthe filter bed, they form a crust on that surface.

Flowing along with the process liquid, smaller particulates may becaptured at the bottom surface of the filter, retained by the crustformed by the accumulation of larger particulates. Thus, this crust mayby itself prevent the passage of some of the smaller particulates.Alternatively, the smaller particulates may pass through the crust onthe filter bed's lower surface, penetrate the bed, and become trapped bythe second mechanism, namely, depth filtration, which captures andretains the smaller particles in the interstitial spaces between thefilter media particles forming the bed. The smallest particulates willpass through the crust on the first filter bed's lower surface, the bed14 itself and the bed restraint structure 16. These particulates willthen flow with the liquid out of the filter through the filter housingoutlet 17, conduit 82, the normally-open inlet valve 83 for the secondfilter bed, conduit 84, and finally into the second filter housing 62through the housing inlet 61.

After passing through the inlet 61, the flowing liquid spreads out, andflows vertically upward through the filter housing 62, causing thefilter bed 63, which floats on top of the rising fluid, to rise in thehousing 62. The second filter bed 63 is composed of smaller diameterparticles than the first filter bed 14 (e.g., 0.05 to 0.1 mm). Thesecond filter bed particles are selected to be within the specific sizerange and composition to meet the specific needs of the filtrationprocess as well as having a specific gravity lower than that of theliquid being filtered.

As the process liquid flows into the filter housing 62, the level of theprocess liquid rises in the housing, and the bed 63, floating on therising process liquid, reaches the bed support 64 adjacent the top ofthe filter housing. As described above, this support retains the bedmedia 63, and also provides a final filtration barrier to theparticulates carried in the liquid. The bed support is nominally formedfrom the same kind of multi-layer sandwich 16 previously discussed andillustrated in FIGS. 2 and 3.

As the process liquid flows vertically upward through the filter bed 63,the smallest contaminant particles are retained by the second filter bed63 through both surface filtration and depth filtration mechanisms.After flowing through the bed support 64, the liquid enters the top ofthe filter housing and exits through the exit port 66. The liquid thenflows through a connecting conduit 86 to a normally-open valve 87,another connecting conduit 88, and a flow sensor 27. From the flowsensor 27, the liquid flows through an additional conduit 28 thatconnects to a clean process liquid reservoir 29. Also connected to thisconduit 28 through an additional conduit 31, normally-closed valve 32,and final conduit 33, is the backwash reservoir 34. As the liquid levelin the backwash reservoir 34 recedes and is sensed by level sensor 36,the sensor signals the controller 54 via wire 109 and the controlleradds clean liquid to the reservoir 34 by opening normally-closed valve32 via wire 110. When the liquid level in the backwash reservoir 34 issufficient, the level sensor 36 signals the controller 54 via wire 109and the controller closes valve 32 via wire 110 to stop the flow ofliquid into the reservoir 34.

The backwash process in this embodiment is to clean each bedindividually, routing the dirty liquid from both filters into thecollection tank 48. When backwash operation is required in thisembodiment, the controller 54 closes the normally-open valves 9, 83 inthe first filter inflow line 11, in the second filter inflow line 82,and valve 87, in the filter outflow line 86 via wires 103, 123 and 127,respectively, to prevent continued flow of the liquid through thefilters. The controller 54 opens the normally-closed liquid drain valve46 and the normally-closed atmosphere vent valves 22 via wires 102 and111. With these valves 46, 22 open, dirty liquid drains from the firstfilter housing 13 into the collection reservoir 48 through conduit 11,valve 46 and conduit 47. As the liquid from the first filter housing 13drains into the collection reservoir 48, air enters the filter housingthrough valve 22 and conduit 21, and the liquid level in the housingdrops. When the liquid level reaches the bottom of the bed, the bedmaterial 14 (which has a specific gravity less than one half that of theprocess fluid, and thus is still pressed against the retaining screen 16as it floats on top of the process liquid) begins to descend in thefilter housing 13 as it floats on the top of the receding liquid. Theliquid level is allowed to recede until the top of the filter bed hasdescended below the midpoint of the filter housing, which fact isindicated to the controller 54 by the lower liquid level sensor 18 viawire 106. At this point, the controller 54 closes the drain valve 46 viawire 102 and the backwash process is initiated to clean the filter bed14.

In the backwash process for this embodiment of the invention, cleanliquid from the backwash reservoir 34 is withdrawn through conduit 37 bythe backwash pump 39 and pumped through the supply conduit 41, thenormally-closed Valve 42 which the controller 54 has now opened via wire105, and conduit 43 and then sprayed onto the bed through single ormultiple backwash spray nozzle(s) 44. The number of nozzles 44 isdetermined by the cross-sectional area of the filter bed and theidentity of the bed material. A single wide angle solid cone nozzle witha wide angle of dispersion (e.g. 90 degrees) can easily backwash afilter bed contained in a housing of up to six to eight inches indiameter. Larger diameter housings and smaller particle filter bedsrequire multiple liquid spray nozzles for effective backwashing. Whenthe bed consists of extremely small particles, which may compress duringfiltration, it may be necessary to have one or more additional spraynozzles spray vertically upwardly to help dislodge the compressed bedparticles and wash them into the lower section of the filter housing 13.

As clean liquid is sprayed downward from the nozzle 44, it washesadhering contaminant particulates off each particle of the filter bed14. As this sprayed liquid drains down through the remaining bedmaterial, carrying with it the collected contaminants and any additionalcontaminants that become entrained in the liquid along the way, itaccumulates in the bottom of the housing. As it accumulates, the liquidlevel in the housing rises, and the super-buoyant media bed (floating ontop of the liquid) rises in the housing. As the bed 14 rises, the bedparticles move upward in the housing, moving the bed particles past thebackwash nozzle 44, which is now essentially embedded in the filter bed14, and which continues to spray clean liquid into the bed, thuscontinuously washing out of the filter bed the contaminant particulates.

Because these contaminant particulates are heavier than either theliquid or the bed particles, the liquid spray washes them out of the bedand causes them to sink to the bottom of the filter housing.Simultaneously, the filter bed particles, which are lighter than theprocess liquid, continue to float upwards on the rising liquid level inthe filter housing. The backwash spray is continued until the entire bedhas risen above the nozzle, allowing all of the bed particles to becleansed by the spray of clean liquid emitted by the nozzle 44. Levelsensor 19 indicates to the controller 54 through wire 107 that the levelof liquid in the housing 13 has risen to the highest appropriate level,thus indicating that the entire bed has been washed in this fashion andthat the filter bed now is positioned in the top portion of the filterhousing above the body of contaminated liquid.

When the filter controller receives the signal from level sensor 19 thatthe level is appropriate, the controller 54 opens drain valve 46 viawire 102, and the particulate-laden contaminated liquid drains into thecollection reservoir 48. Such draining may be effected by gravityinduced flow, or a suction pump or siphon tube may be utilized tototally drain the contaminated liquid in less than one minute, causingthe filter bed to descend in the housing as the contaminated liquidrecedes.

This backwash sequence can then be repeated as necessary to ensure thehighest level of cleanliness in the filter bed. After the backwashprocess is completed, the controller 54 closes normally-closed valves 22and 46 via wires 111 and 102. Once backwashed, the clean filter mediumis then again ready to filter particulates from the process liquidstream.

After the first filter bed 14 is backwashed, the second filter bed 63backwash operation is performed. To backwash the second filter bed 63,the controller 54 keeps the normally-open valves in the filter inflowline 83 and in the filter outflow line 87 closed to prevent continuedflow of the liquid through the filter. The controller 54 then opens thenormally-closed liquid drain valve 91 and the normally-closedatmospheric vent valve 71 via wires 122 and 126. With these valves open,dirty liquid drains from filter housing 62 into the collection reservoir48 through conduit 84, valve 91 and conduit 47. As the liquid from thesecondary filter housing 62 drains into the collection reservoir 48, airenters the filter housing through valve 71 and conduit 69, and theliquid level in the housing drops.

When the liquid level reaches the bottom of the bed, the bed materialbegins to descend in the filter housing 62 as it floats on the top ofthe receding liquid. The liquid level is allowed to fall until the topof the filter bed has descended below the midpoint of the filterhousing, as indicated to the controller 54 by the lower liquid levelsensor 67 via wire 124. At this point, the controller closes drain valve91 via wire 122 and the backwash process is initiated to clean thefilter bed.

In the backwash process, clean liquid from the backwash reservoir 34 iswithdrawn through conduit 37 by the backwash pump 39 and pumped throughthe supply conduit 41, the normally-closed valve 76 which the controllerhas now opened via wire 121, and conduit 93 and then sprayed onto thebed through single or multiple backwash spray nozzle(s) 78. The numberof nozzles 78 is determined by the cross-sectional area of the filterbed and the identity of the bed material. When the bed consists ofextremely small particles, which may compress during filtration, it maybe necessary to have one or more additional spray nozzles sprayvertically upward to help dislodge the compressed bed particles and washthem into the lower section of the filter housing 62.

As clean liquid is sprayed downward from the nozzle 78, it washesadhering contaminant particulates off each particle of the filter bed63. As this sprayed liquid drains down through the remaining bedmaterial, carrying with it the collected contaminants, it accumulates inthe bottom of the housing. As it accumulates, the liquid level in thehousing rises, and the super-buoyant media bed (floating on top of theliquid) rises in the housing. As the bed rises, the bed particles moveupward in the housing, moving the bed particles past the backwash nozzle78 which continues to spray clean liquid into the bed, thus continuouslywashing out the contaminant particulates and causing them to sink to thebottom of the filter housing 62. Simultaneously, the filter bedparticles, which are lighter than the process liquid, continue to floatupward on the rising liquid level in the filter housing.

The backwash spray is continued until the entire bed has risen above thenozzle, allowing all of the bed particles to be cleansed by the spray ofclean liquid emitted by the nozzle 78. Level sensor 68 indicates to thecontroller 54 through wire 125 that the level of liquid in the housing62 has risen to the appropriate level, thus indicating that the entirebed has been washed in this fashion and now lies above the contaminatedbody of liquid. When the filter controller 54 receives information fromthe level sensor 68 that the level of the contaminated liquid isappropriate, it opens drain valve 91 via wire 122, and all theparticulate-laden liquid once more drains into the collection reservoir48. This backwash sequence can then be repeated as necessary to ensurethe highest level of cleanliness in the filter bed. The backwashed,clean filter medium is then again ready to filter particulates from theprocess liquid stream.

After backwashing of both filter beds 14 and 63 is completed, thefiltration process is again initiated when the controller 54 closesvalves 91 and 71 via wires 122 and 126, opens the inlet valves 9 and 83and exit valve 87 via wires 103, 123 and 127, respectively, and pumpsliquid from the reservoir 2 via the primary fluid pump 7. As processliquid again enters the housings, the filter beds 14, 63 rise in thehousings and stabilize when they encounter their respective filter bedrestraint structures 16, 64. The filtration process then begins onceagain as the process liquid begins to flow upward through the stabilizedfilter beds.

Filtration of Dissolved Metals

In this embodiment, illustrated diagrammatically in FIG. 10, two filterhousings 13 and 62 are arranged in series as described above withrespect to FIG. 9, and function by a unique method of chemicalprecipitation of dissolved, ionized metals in the aqueous solutions,followed by filtering of and removal of the precipitated particulatesfrom the process liquid with a particulate filter as previouslydiscussed. This is in contrast to dissolved metals conventionallyprecipitated in a liquid containing them by the direct addition of basicsolutions (e.g., lime, sodium hydroxide, potassium hydroxide), whichprovide the required hydroxyl ions for initiation of the precipitationreaction. This addition of basic solutions is usually accomplishedconventionally by using a metering pump to inject precise amounts of thebasic solution into the process liquid stream as it enters a reactor,which serves to ensure sufficient mixing for the metal hydroxides toform and precipitate. These precipitates are subsequently captured by aparticulate filtration system.

The advantage of the metals removal system described herein, in contrastto the conventional method described above, is that no basic solutionsneed be added to cause the precipitation. Instead, the hydroxyl ions aregenerated directly in the process liquid by pumping the liquid throughan ultraviolet radiation reactor. This ultraviolet radiation formshydroxyl ions in the metal-containing aqueous solution. These hydroxylions chemically combine with the ionized metals and cause them toprecipitate and form particulates. These particulates are then removedfrom the aqueous solution by the filter bed filtration embodimentsdescribed herein.

A diagram of a system to effect this type of precipitation is presentedin FIG. 10. The diagram presented in this figure illustrates a pair offilter beds connected in series as described above and illustrated inFIG. 9. In FIG. 10, however, an ultraviolet reactor 191 has been addedto the system to process aqueous solution exiting from the first(coarse) filter housing 13. Except for the addition of the ultravioletreactor 191, the structure and operation of the system of FIG. 10 is inall respects similar to the structure and operation of the systemillustrated in FIG. 9 and described hereinabove. Accordingly, in theinterest of brevity in this description, the operation of the system ofFIG. 10 will not be described in detail and the description of thesystem illustrated in FIG. 9 is incorporated herein by reference. Inthis embodiment, suffice to say that both the smallest particulate andthe dissolved metals will flow with the liquid out of the filter housing13 through the filter housing outlet 17 and will proceed through conduit82.

The aqueous process liquid then flows through an ultraviolet (UV)exposure reactor 191, where it is exposed to a high flux of UVradiation. The UV radiation induces the formation of hydroxyl ions inthe liquid, which subsequently combine with the ionized metals in thesolution to form insoluble precipitate particles. The liquid then flowsout of the UV exposure reactor 191, through the normally-open inletvalve 83 for the second filter bed, conduit 84, and into the secondfilter housing 62 through the housing inlet 61. The process liquid, nowbearing the insoluble precipitated particles passes upward through thefilter bed 63 in the second filter housing 62 as previously described.

While the invention has been described as having specific embodiments,it will be understood that it is capable of further modification. Thedisclosure herein is therefore intended to cover any variations, uses,or adaptations of the Invention as come within the scope of the appendedclaims. Accordingly, having described the invention, what is believed tobe new and novel and sought to be protected by letters patent is asfollows.

1. In a process liquid filtration apparatus embodying a filter bed forremoving particulates from a process liquid having a predeterminedspecific gravity, a filter bed comprised of super-buoyant particleshaving a specific gravity lower than one half of the predeterminedspecific gravity of the process liquid.
 2. The filter bed according toclaim 1, wherein said super-buoyant filter bed particles are looselycompacted and a majority of their mass floats on top of the processliquid to be filtered.
 3. The filter bed according to claim 1 whereinsaid mass of super-buoyant filter particles is sufficiently looselycompacted to enable backwashing of the filter bed as the mass of filterparticles floats on a body of process liquid.
 4. The filter bedaccording to claim 1, wherein said super-buoyant filter bed particlesare selected to be a specific size within the range of 0.1 micron and25.4 mm.
 5. The filter bed according to claim 1, wherein saidsuper-buoyant filter bed particles are selected to be a specific sizewithin the range of 1.0 and 25.4 mm for a coarse filter.
 6. The filterbed according to claim 3, wherein said mass of super-buoyant filterparticles expands in volume from about 10 to 30% during said backwashingto thereby free captured particulates and washing them out of the filterbed.
 7. The filter bed according to claim 1, wherein said super-buoyantfilter bed particles are selected from a group consisting of plastic,glass or ceramic.
 8. The filter bed according to claim 1, wherein saidsuper-buoyant filter bed particles are selected to be a specific sizewithin the range of 0.1 micron and 1.0 mm for a finer filter.
 9. Thefilter bed according to claim 1, wherein said super-buoyant filter bedparticles are selected to be a specific size that will require a processfluid pressure of from approximately 20 to 150 psi for process fluid toflow through said filter bed.
 10. The filtration apparatus according toclaim 1, wherein said filtration apparatus includes an ultravioletreactor, said process liquid is caused to flow through said ultravioletreactor to be exposed to a high flux of ultraviolet radiation to inducethe formation of hydroxyl ions in the process liquid which combine withionized metals in said process fluid to form insoluble precipitateparticles, whereupon said process liquid bearing said precipitatedparticles is pumped through said filter bed to remove said precipitatedparticles.
 11. The method of filtering contaminated particulates from aprocess liquid having a predetermined specific gravity to enable re-useof the filtered and de-contaminated process liquid, comprising: a)drawing particulate contaminated process liquid from a source thereof;b) applying pressure to the particulate contaminated process liquiddrawn from said source; c) delivering an initial quantity of saidpressurized particulate contaminated process liquid into a filterchamber having an inlet port, an outlet port and a composite filter bedformed by distinct super-buoyant filter particles having a specificgravity lower than one half that of the said predetermined specificgravity of said process liquid whereby said filter bed has the capacityto float on top of said process liquid; d) continuing the delivery ofsaid pressurized particulate contaminated process liquid into the inletport of said filter chamber to effect displacement of said compositemass of distinct filter particles comprising said filter bed fromadjacent said inlet port to adjacent said outlet port where displacementof said filter bed is terminated; e) continuing the delivery of saidpressurized particulate contaminated process liquid into said filterchamber after displacement of said filter bed has terminated, wherebycontinued delivery of said pressurized process liquid into said filterchamber results in said process liquid being forced to flow through thenow stationary composite mass of distinct super-buoyant filter particleswhereby said particulates are captured and retained by said compositemass of distinct filter particles; and f) discharging filtered andde-contaminated process liquid from said filter chamber through saidoutlet port and delivery to at least one storage reservoir.
 12. Themethod according to claim 11, wherein said filtered and de-contaminatedprocess fluid is selectively delivered to one of two storage reservoirshaving inlet and outlet ports.
 13. The method according to claim 11,wherein a pump is provided having an inlet port connected to said sourceof particulate contaminated process liquid and an outlet port connectedto the inlet port of said filter chamber.
 14. The method according toclaim 11, wherein the pressure applied to said particulate contaminatedprocess liquid ranges selectively from approximately 20 to 150 psi. 15.The method according to claim 11, wherein particulates larger in sizethan the interstices of said super-buoyant filter bed are filtered fromsaid process liquid by the mechanism of surface filtration wherein saidlarger particulates adhere to the upstream surface of said filter bedand form a crust thereon through which smaller particulates penetrate.16. The method according to claim 11, wherein particulates smaller insize than the interstices of said filter bed are filtered from saidprocess liquid by the mechanism of depth filtration wherein said smallerparticulates are captured and retained in the interstitial spaces in thefilter bed between the distinct filter bed particles.
 17. The methodaccording to claim 11, wherein at least a portion of said filtered andde-contaminated process liquid discharged from said filter chamber isselectively directed into a backwash reservoir for storage and selectivere-use in backwashing said filter bed to remove accumulated particulatestherefrom.
 18. The method according to claim 11, wherein the flow rateof process fluid exiting the filter chamber is sensed, measured andcompared over time with the flow rate of process liquid exiting thefilter chamber at the commencement of a filtering cycle to determine theresistance to the flow of process liquid through said super-buoyantfilter bed and upon reaching a predetermined resistance level correlatedto a specific low rate of flow of said process liquid a backwash cycleis initiated to remove particulates adhering to said filter bed.
 19. Themethod according to claim 18, wherein when said predetermined resistancelevel is reached, delivery of said particulate contaminated processliquid to and from said filter chamber is temporarily discontinued, theparticulate-laden process liquid in said filter chamber is drained intoa reservoir whereupon said composite filter bed is displaced to adjacentsaid inlet port of the filter chamber following which cleannon-contaminated process liquid is sprayed onto the compositesuper-buoyant filter bed to backwash therefrom particulate contaminantspreviously filtered from said process liquid, then draining the filterchamber of particulate contaminated backwash process liquid, andthereafter re-initiating delivery of particulate contaminated processliquid to said filter chamber to commence another filtering cycle. 20.The method according to claim 19, wherein backwashing of said filter bedis initiated automatically when said super-buoyant filter bed has beendisplaced to a predetermined level within said filter chamber adjacentsaid inlet port whereupon spraying of clean non-contaminated processliquid onto said filter bed is initiated.
 21. A liquid filtrationapparatus for removing particulates from a process liquid having apredetermined specific gravity, comprising: a) a source of saidparticulate laden process liquid; b) a filter chamber having an inletport for receiving said particulate laden process liquid and an outletport for discharging filtered process liquid therefrom; c) a compositefilter bed within said filter chamber formed by distinct super-buoyantfilter particles having a specific gravity lower than one half that ofthe said predetermined specific gravity of said process liquid; d) meansfor conveying particulate laden process liquid into said filter chamberfrom said source thereof for passage through said compositesuper-buoyant filter bed for separation of said particulates from saidprocess liquid and discharge of filtered process liquid through saidoutlet port of said filter chamber; and e) means communicating with saidoutlet port for conveying said filtered process liquid away from saidfilter chamber for re-use as a non-contaminated process liquid.
 22. Theliquid filtration apparatus according to claim 21, wherein a storagereservoir is provided having an inlet port to selectively receivefiltered process liquid from said filter chamber and an outlet port forselectively delivering filtered process liquid back to said filterchamber for backwashing said composite filter bed to remove particulatestherefrom.
 23. The liquid filtration apparatus according to claim 22,wherein a storage reservoir is provided connected to said inlet port ofsaid filter chamber to selectively collect particulate contaminatedprocess liquid from said filter chamber following backwashing of saidcomposite filter bed to remove said particulates.
 24. The liquidfiltration apparatus according to claim 21, wherein control means areprovided selectively operable to control the delivery of particulatecontaminated process liquid to and from said filter chamber and tocontrol the discharge of filtered process liquid from said filterchamber.
 25. The liquid filtration apparatus according to claim 21,wherein means are provided within said filter chamber for preventingsaid super-buoyant filter bed particles from being discharged from saidfilter chamber.
 26. The liquid filtration apparatus according to claim21, wherein said filter chamber is provided with a normally closed venttube communicating the interior of said filter chamber to the atmosphereand selectively opened when particulate contaminated process liquid isdrained from said filter chamber following backwashing of said compositefilter bed to remove contaminating particulates therefrom.
 27. Theliquid filtration apparatus according to claim 21, wherein at least onebackwash spray head is mounted within said filter chamber, meansconnecting said at least one backwash spray head to the outlet port ofsaid filter chamber to convey filtered process liquid from said filterchamber to said at least one backwash spray head, and means interposedin said means connecting said at least one spray head to said filterchamber selectively operable to initiate conveyance of said filteredprocess liquid to said at least one spray head when said super-buoyantfilter bed is so clogged by particulates that the rate of flow of saidfiltered process liquid drops below a selected predetermined flow rate,whereby said filter bed is backwashed to remove said particulatestherefrom.
 28. The liquid filtration apparatus according to claim 27,wherein said means responsive to said reduced flow rate from said filterchamber includes a sensor that measures said flow rate, a plurality ofsolenoid operated valves, a filtered process liquid reservoir, a pumpand an electronic control system interconnecting said sensor, valves,reservoir and pump.
 29. The liquid filtration apparatus according toclaim 21, wherein dual filter chambers are provided connected in aparallel flow filtration system configuration.
 30. The liquid filtrationapparatus according to claim 29 wherein control means are providedoperable to retain one filter chamber in filtering operation while thefilter bed of the other filter chamber is being backwashed, whereby saidparticulate contaminated process liquid may be filtered continuouslywithout interruption.
 31. The liquid filtration apparatus according toclaim 28, wherein dual filter chambers are provided connected in aparallel flow filtration system configuration, and said electroniccontrol system comprises an embedded microprocessor operable to monitorsaid sensors and to turn “ON” and “OFF” in a timely manner all of thepumps and valves required to operate the dual filter chamber apparatus.32. The liquid filtration apparatus according to claim 21, wherein dualfilter chambers are provided connected in a series flow filtrationsystem configuration wherein a first of said filter chambers is theprimary filter chamber and a second of said filter chambers is thesecondary filter chamber.
 33. The liquid filtration apparatus accordingto claim 32, wherein the outlet port of said primary filter chamber isconnected to the inlet port of said secondary filter chamber, the outletport of said secondary filter chamber is selectively connected todeliver filtered process liquid to said primary and secondary chambersto effect backwashing of the composite filter beds in said dualchambers, and an electronic control system is provided interconnectingsaid series flow filter chambers whereby the filter beds in saidseries-connected filter housings may be composed of particles sized tofilter coarse particulates from process liquid passing through saidfirst filter chamber and composed of particles sized to filter finerparticulates from the process liquid admitted to said secondary filterchamber to thus maximize the total amount of contaminant particulatesremoved by liquid filtering apparatus.
 34. The liquid filtrationapparatus according to claim 33, wherein a hydroxl ion-generatingultraviolet reactor is interposed between said primary and secondaryfilter chambers, said filtered process liquid discharged from saidprimary filter chamber flows through said ultraviolet reactor and isexposed to a high flux of ultraviolet radiation in flowing therethroughwhich induces the formation of hydroxl ions in the process liquid whichcombine with ionized metals in the process liquid to form insolubleprecipitate particles which flow into the secondary filter chamber to becaptured by said composite super-buoyant filter bed and filtered fromthe process liquid flowing through said secondary filter chamber. 35.The liquid filtration apparatus according to anyone of claims 21, 22,23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33 or 34, wherein said compositesuper-buoyant filter bed particles are selected from a group consistingof plastic, glass or ceramic and selected to be a specific size withinthe range of 0.1 micron and 25.4 mm.
 36. The liquid filtration apparatusaccording to anyone of claims 21, 29 or 32, wherein each said filterchamber is symmetrical about a vertical axis, said inlet and outletports are coincident with said vertical axis, said compositesuper-buoyant filter bed is initially contained within said filterchamber adjacent said inlet port and buoyantly floats upwardly on saidprocess liquid to adjacent said outlet port by the process liquidadmitted into said chamber through said inlet port and floats downwardlyon the surface of said process liquid when said process liquid isdrained from said filter chamber in preparation of backwashing saidcomposite filter bed and subsequently floats upward during saidbackwashing cycle.